Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 413 PM EST Thu Feb 28 2019 Valid 00Z Fri Mar 01 2019 - 00Z Mon Mar 04 2019 ...California across Great Basin to Central Rockies... Days 1-3... A broad southern stream trough over northern CA this afternoon with a powerful zonal jet produces heavy snow over terrain UT/CO tonight with snow elevations generally 7000ft. QPF of a half inch over UT produces moderate probabilities for 8 inches over the Wasatch into the Uintas tonight and up to one inch over CO brings moderate to high probabilities for 12 inches over the Rockies. Low pressure off the OR coast through Friday and another low over south-central Canada through Saturday allows the mainly zonal southern jet stream to persist over the CONUS with an embedded low crossing CA Saturday and reaching the central Rockies Saturday night. Pacific moisture ahead of this low will create heavy Day 2 snow across the Sierra Nevada where snow elevations will generally be 5000 to 7000ft from north to south. The fairly tight moisture corridor along with jet diffluence will spread heavy snow farther east across NV/UT/CO with snow elevations also 5000 to 7000ft north to south across the zone. Impressive two day totals along this swath feature high probabilities for 18 inches in the southern Sierra Nevada on Day 2 and for the central Rockies on Day 2.5. Lighter accumulations are expected in the lower mountains along this swath with moderate to high Day 2.5 probabilities for 6 inches. ...Northern Plains to the Great Lakes... Days 1-2... A shortwave ejects east from the low off the OR coast and is directed south of the south-central Canadian low allowing a swath of locally moderate snow from the high plains of norther MT across SD Friday before weakening as it crosses the central Great Lakes Friday night. Moderate to high probabilities for 6 inches are over northern MT (where upslope flow persists on Day 1), with low to moderate probabilities for 4 inches across southern MT and SD also on Day 1. ...Mid-Atlantic and Northeast... Days 1-2... A weak shortwave trough will shift east in zonal flow from OH tonight as 1026mb surface high pressure centered over New England drifts east. WAA and a brief period of diffluence within a weakly coupled jet structure and short but robust mid-level frontogenesis will produce a light wintry mix over the central Mid-Atlantic overnight ahead of the shortwave which will enhance cold air damming from the high to the north. This will enhance the wintry mix which looks to be mainly snow over the DC area late tonight and become a wintry mix Friday as a second shortwave trough pushes east from KY/TN. WAA should allow a change to plain rain from SE to NW, but pockets of freezing rain look to persist near the MD/PA border into Friday night. There is a Day 1 moderate probability for a tenth inch of ice in the Allegheny highlands of WV/VA and moderate probability for 4 inches of snow along the western MD/PA border. Farther northeast across coastal northern Mid-Atlantic to southern New England both waves bring light precip with the second allowing a coastal low to develop Saturday with the 12Z ECMWF/UKMET preferred for a near coastal light snow. Moderate probabilities for two inches are across southern New England which includes the farther inland solution of the 12Z GFS which was not preferred. ...Central Plains to Ohio Valley... Day 3... The mid-level trough crossing from CA Saturday will ride a 120+kt Pacific Jet across CO Saturday night. At the same time, a cold front will be dropping through the Plains producing a tightening baroclinic gradient. This baroclinic gradient will be acted upon by the aforementioned upper forcing and an increasingly coupled jet structure to produce surface cyclogenesis which will begin late Saturday night over the TX Panhandle. Mid-level confluence will drive Pacific Moisture into the region, which will be wrung out as precipitation in response to increasing synoptic lift, aided by isentropic ascent on low-level warm advection and intensifying mid-level frontogenesis. This all suggests a band of heavy snow will spread west to east from eastern CO through KS/MO and up the OH Valley Sunday. Given the zonal flow, little perturbations will cause the low track to waver considerable. As of now Day 3 WPC probabilities are moderately high for 4 inches across KS to southern OH. On the southern fringe of this snow swath, isentropic lift atop the cold surface high will likely produce freezing rain. Day 3 probabilities are low for a tenth inch from OK across southern MO to southern IN. Jackson